Caption: Computer simulation of conditions inside a tokomak reactor. This simulation shows something of the electromagnetic conditions inside a 'doughnut'- shaped tokomak vessel. The multi-coloured band is aligned with the local magnetic field, the colour represents the electrostatic potential at each point. The yellow trajectory is the orbit of a single ion. The red grid is a cross-section of the tokomak, used as a reference to determine any drift in the beam. This type of simulation is used by physicists to predict the behaviour of super- hot plasma inside any design of tokomak reactor, the favoured design for nuclear fusion reactors.